Synthetic resin bottle with circumferential ribs for increased surface rigidity

ABSTRACT

The technical problem of this invention is to eliminate the need to use deformable panel walls and to find the body of a shape that no false deformation, such as dented deformation, takes place in a portion of the body due to the hot filling of the contents or the reduced pressure created by the treatment of retort-packed foods. The object of this invention is to obtain a bottle that can inhibit the deformation caused by reduced pressure, has a high buckling strength, and is good in outer appearance. As the solution, there is provided a biaxially drawn, blow-molded bottle made of a synthetic resin, in which the surface rigidity of the wall of body is set in such a manner that a part of the body wall cannot become dented inward under a reduced inner pressure of at least 350 mmHg (46.7 kPa).

TECHNICAL FIELD

This invention relates to a biaxially drawn, blow-molded bottle made ofa synthetic resin, especially made of a polyethylene terephthalate resinfor use in hot filling of the contents.

BACKGROUND OF THE INVENTION

The biaxially drawn, blow-molded bottle of a polyethylene terephthalateresin (hereinafter referred to as the PET resin) can be given a thin anduniform wall thickness because of distinguished characteristics of PET.Since such bottles are economical, have high resistance to contents anda high mechanical strength, and have good outer appearance, the bottlesare widely used as liquid containers in various fields.

As described above, the PET bottle has a high mechanical strengthdespite its thin wall. However, since the body, a major part of thebottle, has a thin wall, the bottle is inconvenient in that a part ofthe body may falsely become dented and deform under a reduced pressurecreated inside the bottle and may give a marked damage to the outerappearance of the bottle. As a commercial product, the bottle may bequite poor in appearance.

Especially in recent years, widely spreading applications require thebottles to be hot-filled with beverages at a temperature in the range of85 to 95° C. After the hot filling, the bottles are found to be at agreatly reduced inner pressure once the bottles have been cooled. Thus,there is an ever-increasing request for the bottles that can beprevented from being deformed under such a reduced pressure.

In the applications requiring sterilization of retort-packed foods,e.g., by heating the foods at 121° C. for 30 minutes after the bottlehas been filled with the contents, the resin for molding the bottle mustbe resistant to this temperature, and in addition, the bottle should beable to stand up to severe depressurization.

In order for the PET bottle to be protected from the disadvantage ofdeformation under reduced pressure, various proposals have been made forthe PET bottles. For instance, utility model laid open No. 1982-199511discloses a number of deformable, slightly hollowed panel walls, whichare disposed in the body of the bottle and easily become further dentedinward so as to absorb a negative pressure created inside the bottle.Since the deformable panels become dented to a certain shape, otherportions of the body are protected from false dented deformation underreduced pressure. Thus, the body of the bottle is prevented from showingpoor outer appearance.

However, the deformable panel walls in the above-described conventionalart has a problem in that the extent to which negative pressure can beabsorbed is not sufficient, considering the extent of dented deformationcreated under the reduced pressure. This is because the deformablepanels have been molded beforehand simply in the shape slightly dentedinward so that the dented deformation may occur easily under the reducedpressure created inside the bottle.

Another problem of the deformable panel walls is that the body has adecreased buckling strength due to the existence of these deformablepanels, which are molded by denting and deforming a part of the wallsand which are equally spaced in a row around the circumference of thebody.

Still another problem of the deformable panels is that the bottlesometimes looks poor in appearance. Since the deformable panel wallsthat become dented are longer than are wide, the portion of the bodysurrounded by the deformable panels looks quite lean as compared withother portions of the body, depending on the angle from which the bottleis viewed.

Lastly, there is a problem that the bottle becomes permanently deformed.All of those bottles causing a reduced pressure to be created inside arefilled with hot liquid contents. Initially when the bottle is filledwith the hot contents and sealed, the inside of the bottle is put undera pressurized condition. Therefore, the deformable panel walls are alsorequired to have an ability to absorb a pressure, in addition to theability to absorb a reduced pressure. Since these deformable panel wallshave a shape of simply curved and dented panels, the panels cannot fullyabsorb the pressure. If a large pressure is applied, the deformablepanels are not elastically inflated but are reversibly projected, andremain permanently deformed.

In spite of these many difficulties, fact is that the above-describeddeformable panels have been and are used in the bottles in most caseswhere an especially severe reduced pressure is derived from the hotfilling using a temperature in the range of 85 to 95° C.

This invention has been made to solve the above-described problemsobserved in the conventional art. Thus, the technical problem of thisinvention is to eliminate the need to use the deformable panel walls andto find the body of such a shape that no false deformation, such asdented deformation, takes place in a portion of the body due to the hotfilling or the reduced pressure created after the treatment ofretort-packed foods. The object of this invention is to obtain a bottlethat can inhibit the deformation caused by reduced pressure, has a highbuckling strength, and is good in outer appearance.

DISCLOSURE OF THE INVENTION

The means of carrying out the invention of claim 1 to solve theabove-described technical problems comprises that the surface rigidityof the body wall has been set in such a manner that a part of the bodywall never becomes dented inward under a reduced inner pressure of atleast 350 mmHg (46.7 kPa).

The above-described configuration of claim 1 is intended to make thebody wall resist a lateral pressure applied onto the wall surface whensuch a pressure is created in the hot filling process by a reducedpressure of at least 350 mmHg (46.7 kPa). This can be achieved byraising the surface rigidity of the body wall to a high level, withoutproviding the deformable panel walls in which a portion of the body wallbecomes dented and deforms as found in the conventional art.

In this configuration, the surface rigidity of the body wall is at workto inhibit the deformation under reduced pressure. Thus, it is possiblewith this configuration to deal with such problems as the deficientdented deformation, insufficient buckling strength, poor outerappearance, and the occurrence of permanent inverted deformation, all ofwhich are caused by the adoption of deformable panels. Bottles that canbe obtained eliminate the need for deformable panels, have quite a newappearance, and are of an elaborate design that differs from the designsused in conventional art.

The synthetic resin bottle of this invention is a biaxially drawn,blow-molded bottle made of especially a PET resin. If necessary,however, polyethylene naphthalate (PEN) or the MXD-6 nylon resin can beblended with the PET resin to improve, for instance, heat-resistingproperty and gas barrier property, within the range in which the natureof the PET resin is not impaired. In another method, PEN or MXD-6 can belaminated as an inner layer between the PET resin layers.

The means of carrying out the invention of claim 2 exists in theconfiguration that the body has a cylindrical shape.

In the configuration of claim 2 where the bottle has a cylindricalshape, the body wall outwardly forms a convex surface, which gives highsurface rigidity to the entire body.

The means of carrying out the invention of claim 3 includes theinvention of claim 1, and also comprises that the body is in a regularpolygonal shape having at least 8 corners.

In the configuration of claim 3, the body shape is not limited to acylindrical shape, but a regular polygonal shape can also be used,provided that the regular polygon has 8 or more corners. The reason isthat, with a regular polygon having 7 corners or less, each of the flatpanel wall surfaces disposed around the body has laterally such a largewidth that the panel tends to become dented and deform easily underreduced pressure.

The means of carrying out the invention of claim 4 exists in theconfiguration that, in the invention of claim 2 or 3, two or moregroove-like ribs are disposed circumferentially around the body. Amongthe circumferential ribs, the uppermost rib is disposed at the upper endof the body near the border with the shoulder that has a roughlytruncated conical shape. The lowermost rib is disposed at the lower endof the body. Distance H between two adjacent ribs is set at a length inthe range of 0.2D to 0.6D where D indicates the diameter of thecylindrical body or the length of a diagonal line of the cylindricalbody having a regular polygonal shape.

In the configuration of claim 4, the uppermost circumferential rib isdisposed at the upper end of the body near the border with the shoulderthat has a roughly truncated conical shape. Therefore, it is possible toinhibit effectively the dented deformation, which is apt to take placeon or near this border.

The body can be equipped with a number of circumferential ribs,including those disposed at the upper end and the lower end of the body,so that the body wall has an increased level of surface rigidity.

The circumferential ribs are required to resist the lateral pressurecreated under reduced pressure. The interval between two adjacent ribscan be set advantageously at 0.6D or less though it depends on thethickness of the body wall. At this interval, increased surface rigiditycan be achieved for the same thickness as that of the hot-filled bottlesprovided with conventional deformable panels. At the interval of 0.2D orless, the circumferential ribs are too close to adjacent ribs, resultingin the lack of smooth outer surface. Under this condition, the body ofthe bottle is found inconvenient to attach a label. If the bottle iscovered with shrink film, the body is also inconvenient to clearly showthe name of the merchandise or to decorate the bottle.

The means of carrying out the invention of claim 5 exists in theconfiguration that, in the invention of claim 4, the distance H betweentwo adjacent ribs is set at a length in the range of 0.3D to 0.45D.

In the above-described configuration of claim 5, the bottle is allowedto have a thinner wall than the bottle in conventional art. At the samewall thickness, the bottle according to claim 5 can be used at a higherhot-filling temperature or under a severer pressure condition than inconventional art. The circumferential ribs can be disposed in a smallernumber, which gives the bottle preferable outer appearance.

The means of carrying out the invention of claim 6 exists in theconfiguration that, in the invention of claim 1, 2, 3, 4, or 5, the wallof the body excluding the neck has a minimum thickness of 300 μm ormore.

In the above-described configuration of claim 6, the surface rigidity ofthe bottle can be raised by giving a large thickness to the bottle, butthe wall thickness has a limit of its own because of preformproductivity, the increase in material cost, and an increased bottleweight. A suitable wall thickness is a minimum of 300 μm or more, andpreferably ranges from 350 to 650 μm on an average. At a thickness lessthan 300 μm, it becomes difficult to secure the surface rigidity thatcan resist the depressurization.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a front elevational view of an entire synthetic resin bottlein the first embodiment of this invention.

FIG. 2 is a front elevational view of an entire synthetic resin bottlein a comparative example as compared with the first embodiment shown inFIG. 1.

FIG. 3 is a front elevational view of an entire synthetic resin bottlein the second embodiment of this invention.

FIG. 4 is a front elevational view of an entire synthetic resin bottlein the third embodiment of this invention.

FIG. 5 is a front elevational view of an entire synthetic resin bottlein the fourth embodiment of this invention.

PREFERRED EMBODIMENTS OF THE INVENTION

This invention is further described with respect to preferredembodiments, now referring to the drawings. FIG. 1 is a front view of anentire synthetic resin bottle in the first embodiment of this invention.It is an ordinary 200-ml PET bottle, which has been biaxially drawn andblow-molded. In its structure, the bottle comprises cylindrical body 2,shoulder 4 of a truncated conical shape disposed at the upper end of thebody 2, short cylindrical neck 3 disposed on the shoulder 4, and bottom7 at the lower end of the body 2. The bottle 1 has the cylindrical body2 with a diameter of 54 mm, and has a total bottle height of 140 mm. Thebody 2 has an average thickness of 350 μm and a minimum thickness of atleast 300 μm.

The body 2 is provided with a total of four circumferential ribs 5having a cross-section of almost U-shape. Among these ribs, theuppermost rib is disposed at the upper end of the body 2 near the borderwith the shoulder 4. The lowermost rib is disposed at the lower end ofthe body 2 near the border with the bottom 7. The distance H between twoadjacent ribs 5 is 24 mm (0.44D).

FIG. 2 shows a bottle of a comparative example having threecircumferential ribs 5, the least number of ribs as compared to thefirst embodiment. The distance H is 36 mm (0.67D).

The bottle of the first embodiment and the bottle of the comparativeexample were put to a hot-filling test at 87° C. After the bottles 1were cooled down to room temperature, they were checked for deformation.No dented deformation was observed in the bottle 1 of the firstembodiment. On the other hand, the bottle 1 of the comparative exampleshowed notable dented deformation in the wall of the body 2.

The bottle of the first embodiment was also put to one more testconducted at 95° C. No dented deformation was likewise observed in thebottle 1 of the first embodiment as was in the test conducted at 87° C.

The above-described bottles 1 of both the first embodiment and thecomparative example were measured for depressurization strength. Theneck 3 of the bottles 1 was sealed, and the bottles 1 were graduallydepressurized, using a vacuum pump. The extent of depressurization isdefined as the depressurization strength (mmHg, kPa) measured at thetime when a part of the wall surface of the body 2 becomes sharplydented and deforms. The bottle 1 of the first embodiment had adepressurizing strength of 360 mmHg (48.0 kPa), and the bottle 1 of thecomparable example had a corresponding strength of 310 mmHg (41.3 kPa).

As described above, the results of the tests with the bottle 1 of thefirst embodiment indicate that, if there is a distance H of 0.43Dbetween two adjacent circumferential ribs, the bottle 1 of the firstembodiment has the surface rigidity enough to be able to cope with thepressure reduction of at least 350 mmHg (46.7 kPa) at an average wallthickness of 350 μm, which is similar to the wall thickness ofconventional bottles now in use. It is also found that the bottle 1 ofthe first embodiment is fully capable of inhibiting the denteddeformation caused by the pressure reduction during the hot-fillingprocess using a temperature even in the range of 85 to 95° C.

Bottles used for retort-packed foods are thermally treated at 121° C.for 30 minutes. Highly heat-resistant PET bottles are used in such anapplication, and these bottles are molded by the so-called “double blow”method (See patent publication No. 1992-56734).

More particularly, the above-described double blow molding methodcomprises a primary blow-molding step, in which preform having apredetermined shape is biaxially drawn and blow-molded into the primaryintermediate product, a step of heating the primary intermediate productto shrink it thermally and to mold it into the secondary intermediateproduct, and lastly a secondary blow-molding step to mold the secondaryintermediate product into a bottle. The primary intermediate product isheated and is subjected to thermal shrinkage because this heating stepserves to eliminate the residual strain that has been created within theprimary intermediate product and to obtain a highly crystallized andquite highly heat-resisting bottle.

FIG. 3 shows a synthetic resin bottle in the second embodiment of thisinvention. The bottle 1 has been molded under the conditions of aprimary mold temperature of 180° C., a heating temperature of 230° C.,and a secondary mold temperature of 140° C., so that the bottle 1 canrespond to the retort treatment where the bottle and the contents areheat-treated at a temperature of 121° C. for 30 minutes. The bottle 1has an average wall thickness of 400 μm, as compared to 350 μm in thebottle of the first embodiment, and is provided with fivecircumferential ribs 5 that are spaced equally, so that the surfacerigidity is increased further. The circumferential ribs have thedistance H of 18 mm (0.33D) between two adjacent ribs 5.

The bottle 1 of the second embodiment was filled with the contents, andthe retort-packed bottle was heat-treated at 121° C. for 30 minutes. Thebottle 1 was then cooled down to room temperature and was checked forany deformation. No dented deformation was observed. This bottle 1 had adepressurizing strength of 525 mmHg (70.0 kPa). Even for the pressurereduction derived from the treatment at such a high temperature,sufficient surface rigidity can be secured within the range of wallthickness that is permissible for the bottle, by setting a suitabledistance H between two adjacent circumferential ribs 5.

The shape of this bottle obviously allows the bottle to be applicablealso as an ordinary hot-filling bottle that has been biaxially drawn,blow-molded and can be heat-treated at a temperature in the range of 85to 95° C. This shape of the bottle is not limited merely to the use asthe retort-treated bottle.

FIG. 4 shows a synthetic resin bottle in the third embodiment of thisinvention. The bottle has an average wall thickness of 350 μm, thecylindrical body 2 with the cross-section of a regular dodecagonalshape, a diagonal length of 54 mm, and five circumferential ribs 5 thatare spaced equally. There was no dented deformation that was caused bythe hot filling at a temperature of 87° C.

The circumferential ribs 5 are spaced equally in all of the first,second, and third embodiments. However, it is noted that these ribs neednot necessarily be spaced equally. If they are not spaced equally, thepurpose of this patent application can be achieved at the widestdistance H in the range of 0.2D to 0.6D, and more preferably in therange of 0.3D to 0.45D, between two adjacent circumferential ribs 5.

FIG. 5 shows a synthetic resin bottle in the fourth embodiment of thisinvention. Two circumferential ribs 5 are disposed at the upper end andthe lower end, respectively, of the body 2. Between these two ribs, aspiral rib 6 is dug in the wall as a variation of the thirdcircumferential rib 5, but has the same cross-sectional structure asother ribs 5. Thus, the bottle of the third embodiment gives a newappearance of unique design.

Like this embodiment, the circumferential ribs 5 need not necessarily beprepared separately, but the spiral rib 6 in the fourth embodiment maybe adopted within the realm of surface rigidity that can be effectivelystrengthened. At that time, only the distances H1, H2, and H3 shown inFIG. 5 need be taken into consideration. In this embodiment, the widestdistance H1 is 27 mm (0.5D).

The body in the fourth embodiment had a diameter D of 54 mm and anaverage wall thickness of 350 μm. There was no dented deformation thatwas caused by the hot filling at the temperature of 87° C.

In order for the circumferential ribs 5 to give the right surfacerigidity in all the above-described embodiments, it is preferred thatthese ribs are 1 mm or more in width and depth.

The PET bottles with a capacity of 200 ml were used in the tests foreach embodiment. It goes without saying, though, that the bottlecapacity is not set down specifically as long as the bottles meet therequirements described above.

INDUSTRIAL APPLICABILITY

This invention having the above-described configuration has thefollowing effects:

In the configuration of the invention of claim 1, the surface rigidityof the body wall is at work to inhibit the deformation caused by thedepressurization during the hot-filling process. This configurationenables the bottle to cope with such problems as the deficient denteddeformation, insufficient buckling strength, poor outer appearance, andthe occurrence of permanent inverted deformation under the pressurizedcondition, all of which are caused by the adoption of deformable panels.In addition, bottles that can be obtained eliminate the need fordeformable panels, have quite a new appearance, and are of an elaboratedesign that differs from the designs in the conventional art.

In the invention of claim 2, the body has a cylindrical shape. Thisgives the bottle wall a convex shape over all the body surfaces andkeeps the entire body at a high surface-rigid state.

In the invention of claim 3, the body is a cylinder of a regularpolygonal shape having at least 8 corners. Such a shape makes itpossible to avoid a large decrease in the surface rigidity and to obtaina bottle of unique design having a cylindrical body of the regularpolygonal shape.

In the invention of claim 4 or 5, two or more circumferential ribs aredisposed around the body, and the distance H between two adjacent ribsis set in a certain range. With this configuration, it is possible toincrease the surface rigidity of the body to a level enough to resistthe reduced pressure created during the hot-filling process.

In the invention of claim 6, suitable surface rigidity can be secured bysetting the wall thickness at a minimum of 300 μm or more. In addition,when the bottle wall is set at an average thickness in the range of 350to 650 μm, the suitable surface rigidity can be secured whilemaintaining the preform productivity and restricting the material costand the increased bottle weight.

1. A biaxially drawn, blow-molded bottle made of a synthetic resin,comprising at least two groove-like ribs cut circumferentially into abody of said bottle, with an uppermost circumferential rib beingdisposed at an upper end of the body near a border with a shoulder in aroughly truncated conical shape, and a lowermost circumferential ribbeing disposed in a lower portion of the body, wherein a distance Hbetween two adjacent ribs is set at a length in a range of 0.2D to 0.6Dwhere D indicates a diameter of a cylindrical body or a length of adiagonal line of a body having a regular polygonal shape, and whereinplane rigidity of a body wall is set in such a manner that a part ofsaid body wall cannot be sunken inward at a reduced inner pressure of atleast 350 mmHg (46.7 kPa).
 2. The synthetic resin bottle according toclaim 1, wherein the body of said bottle has a cylindrical shape.
 3. Thesynthetic resin bottle according to claim 2, wherein the wall of thebody other than at a neck portion has a minimum thickness of 300 μm ormore.
 4. The synthetic resin bottle according to claim 1, wherein thebody of said bottle is in a regular polygonal shape having at least 8corners.
 5. The synthetic resin bottle according to claim 4, wherein thewall of the body other than at a neck portion has a minimum thickness of300 μm or more.
 6. The synthetic resin bottle according to claim 1,wherein the distance H between two adjacent circumferential ribs is setat a length in a range of 0.3D to 0.45D.
 7. The synthetic resin bottleaccording to claim 6, wherein the wall of the body other than at a neckportion has a minimum thickness of 300 μm or more.
 8. The syntheticresin bottle according to claim 1, wherein the wall of the body otherthan at a neck portion has a minimum thickness of 300 μm or more.